1. Field of the Invention
The present invention relates to an image pickup apparatus capable of picking up a dynamic image or a still image such as a video camera.
2. Related Background Art
In a digital color camera, in response to depressing a RELEASE button, an object image is exposed to a solid-state image pickup element such as a CCD or a CMOS sensor for a desired time period, an image signal thus obtained is converted into a digital signal, and then is subject to predetermined processing such as YC processing, and an image signal of a predetermined format is obtained. This digital image signal is recorded in a semiconductor memory. The recorded image signal can be read according to the need to be reproduced as a signal capable of being displayed or printed, and can be output to a monitor or the like to visualize the recorded image.
Three methods are known for exposing an object image. One is a method in which RGB color filters are formed on a solid-state image pickup element, for example, on a 2×2 pixel basis to give wavelength selectability to each of the pixels, thus separating the object image into RGB images. Another is a method used when a solid-state image pickup element does not have wavelength selectability, in which optical filters having wavelength selectability are inserted in an image pickup optical system, and time-sequential switching of the optical filter is carried out. The third is a method in which a color separation optical system is added at the back of the image pickup optical system to take in images using different image pickup elements with regard to respective wavelength ranges.
A conventional digital color camera often adopts the first method described above. Japanese Patent Application Laid-open No. 9-172649 discloses the third method described above, while Japanese Patent Application Laid-open Nos. 7-84177 and 7-123418 disclose the second method described above.
However, in all three methods described above, since the image pickup optical system is shared by all wavelength ranges, it is necessary to have satisfactory optical performance over the whole visible range. Generally, since an image pickup optical system uses light refraction in optical glass or in optical transparent resin as its imaging principle, the index of refraction changes according to the wavelength, and, in order to prevent the image quality from being degraded due to such change, an optical design method referred to as achromatism is used. As a result, it is difficult to form a high performance image pickup optical system using a simple lens. This is an obstacle to miniaturization of the image pickup optical system.